The invention relates to a bone fixation means of the introductory portion of claim 1.
Such bone fixation means are used, for example, for the medical care of fractures at the proximal femur, particularly of trochanteric fractures and fractures of the neck of the femur. Such devices comprise essentially a bone plate, which can be fixed to the femur with an angular sleeve, which is to be brought into the neck of the femur for accommodating the shaft of the bone fixation means in a rotationally stable manner.
All the known hip screws, which are to be used with bone plates that can be fastened to the femur, have the disadvantage that their out-of-round shaft, which is to be introduced into the sleeve of the bone plate, is firmly connected with the anchoring element (screw or blade) of the bone fixation means.
If, after the implantation of the hip screw, the surgeon wishes to guide the out-of-round sleeve of the bone plate over the out-of-round shaft of the hip screw, then the bone plate of the DHS is not parallel to the femur and, instead, must be rotated into this position, the hip screw, captured in the sleeve, being rotated along. Accordingly, the hip screw is screwed further forward or back a little once again. This advance or retraction is impermissibly large especially in the case of implants employing blades which have a steep pitch, the so-called helical blades.
For hip screws, with a conventional, flat thread, the shaft of the screw can be aligned without problems so that the sleeve tab, when pushed over the out-of-round shaft of the screw, automatically lies parallel to the femur. Normally, once it has been turned upside down over the sleeve, the plate is not rotated further.
In the case of helical blades with a steep pitch (helix), this alignment is difficult, since such implants translate a large distance in or out when rotated only a small amount.